1. Field of the Invention
The present invention relates to a loudspeaker having a magnetic circuits including a plurality of magnets, a voice coil assembly including a plurality of rectangular coils, and a loudspeaker diaphragm to which this voice coil assembly is joined, and the voice coil assembly making up the loudspeaker, and particularly relates to a whole-surface driven, flat thin loudspeaker.
2. Description of the Related Art
Among electrodynamic loudspeakers that convert an audio signal to audio, there is a loudspeaker that employs a plane-type diaphragm as a loudspeaker diaphragm in order to reduce an overall height including magnetic circuits. Although in the plane-type diaphragm, the overall height thereof is lower than that of a cone-type diaphragm, rigidity is insufficient for integral vibration without split vibration. There is a loudspeaker in which bobbins fixed to the plane-type diaphragm have a plurality of voice coils, so that the plane-type diaphragm is vibrated by the plurality of voice coils, thereby suppressing the split vibration. In the related art, as the flat thin loudspeaker having a small overall height, a loudspeaker having a flat diaphragm including a plurality of coils and a magnetic circuit using a plurality of magnets corresponding to the respective coils may be used.
For example, there is a loudspeaker having a thin structure in a drive method of setting many drive points to be close to whole-surface drive, and performing piston movement from a low frequency to a high frequency (Japanese Patent Application Laid-Open No. S57-99898). This loudspeaker has a magnetic circuit group in which a plurality of magnetic circuit units each having at least a pair of two parallel magnetic gaps are arranged in a checkered shape so that the gaps are aligned in parallel in one direction, and one rectangular voice coil is inserted in each of the magnetic circuit units to drive the flat diaphragm.
Moreover, there is a plate-type loudspeaker, in which voice coils are each formed into a square, and the plurality of square voice coils are joined at longitudinal sides and lateral sides to form an aggregate, and this aggregate is attached to a plate diaphragm so that this voice coil aggregate is driven by magnetic circuits (Japanese Utility Model Application Laid-Open No. S55-88590). As shown in FIG. 3 of JP-U No. S55-88590, in this loudspeaker, the plurality of magnetic circuits constructed such that a magnet is sandwiched between one-long-side portions of a pair of belt-like yokes are included, and the numerous magnetic circuits are arranged so that one-side portions of the respective voice coils are inserted between the long-side portions on the other side of the belt-like yokes of these magnetic circuits. In JP-U No. S55-88590, it is described that as to the voice coil aggregate, a coil is wound around a frame body portion to form the voice coil into a square, and then, the plurality of coils are joined at the longitudinal and lateral sides to make up the aggregate.
However, as far as the voice coil aggregate is shown in FIG. 2 of JP-U No. S55-88590, in this voice coil aggregate in the related art, each of the voice coils is wound around an exterior of the frame portion corresponding to a bobbin, and thus, although the adjacent voice coils are joined, the adjacent bobbins making up the voice coil aggregate are spaced by a thickness of linear diameters of the voice coils wound around the exterior, which disables the bobbins to stick together. Furthermore, there is a problem that when the rigidity of the bobbins is insufficient, the bobbins vibrate, resulting in split vibration or that the adjacent bobbins come into contact with each other, thereby causing abnormal noise. Furthermore, in order to solve the problem, an additional heavy substance such as an adhesive to join the adjacent bobbins is needed. As a result, there is a problem that the loudspeaker diaphragm becomes heavier, thereby decreasing reproduction efficiency of the loudspeaker.
Moreover, there is a flat loudspeaker including a bobbin formed of a thin plastic plate by vacuum molding, in which a coil is inserted into a slit of the bobbin (Japanese Patent Application Laid-Open No. S63-299500). Since the coil is arranged in a site of a highest magnetic flux density, that is, a magnetic gap of the magnetic circuit, efficiency of the flat loudspeaker can be increased. In Embodiment 3 shown in FIG. 9 of JP-A S63-299500, there is also disclosed a configuration in which the bobbin is divided into two. In the flat thin loudspeaker having a small overall height, in forming the bobbins to arrange the plurality of coils in the magnetic gaps, a configuration allowing the bobbins to be lightweight and rigid is needed for favorite audio reproduction.
Moreover, as to a damper vibratably holding a voice coil of a loudspeaker, there is disclosed a damper using conductive and elastic phosphor bronze or the like (Japanese Patent Application Laid-Open No. H7-131890). For example, in Embodiment 4 shown in FIG. 5 of JP-A No. H7-131890, loudspeaker dampers 41 are formed by being divided into two using phosphor bronze of a thickness of about 0.1 to 0.5 mm. The use of these loudspeaker dampers 41 can eliminate lead wires that supply audio signals to the voice coils.
The present invention is achieved to solve the problems that the above-described related art has, and an object of the present invention is to realize a whole-surface driven, flat thin loudspeaker that can bring about smooth frequency characteristics with split vibration hardly caused, and, and to manufacture a voice coil assembly that has high reproduction efficiency and fewer operation failures, and further brings about favorite work efficiency in manufacturing and reduced manufacturing cost, and a loudspeaker using the same.